Technical Field
Embodiments of the present invention relate to compositions for application to traveled surfaces for preventing the formation of frozen water, such as ice or snow, on the traveled surface and/or for causing existing frozen water, such as ice or snow, on the traveled surface to melt.
Embodiments of the present invention can also relate to apparatus and systems for determining the amount of a de-icer or anti-icer composition present on a traveled surface and/or for determining the freezing point of liquid on the traveled surface.
Embodiments of the present invention relate to methods for determining the amount of a de-icer or anti-icer composition present on a traveled surface and/or for determining the freezing point of liquid on the traveled surface.
Background of Related Art
Chemical de-icing and anti-icing treatments are routinely used in freezing weather conditions, notably in the winter and in cold climates, to prevent the formation or build up of snow and/or ice on surfaces traversed by pedestrians or vehicles, such as on paths, pavements (sidewalks), stairways, roads, airport taxiways, aprons and runways and the like. Such compositions act by melting existing snow and ice, or by preventing the formation of ice or the settling or build-up of snow, on the surface to which the treatment is applied.
The desirability of maintaining traveled surfaces free from ice, snow or other frozen water (typically derived from freezing precipitation) is well known and understood. Numerous treatments for traveled surfaces are known in the art which are, to a greater or lesser extent, effective in melting ice and snow, or in preventing the formation of ice and snow on the traveled surface.
Known de/anti-icer compositions include freezing point depressant materials as the de/anti-icer moieties or moieties. Numerous freezing point depressant materials are known in the art.
Many prior art de/anti-icer compositions for use on traveled surfaces have contained ethylene glycol. Although ethylene glycol-containing compositions demonstrate high performance with regard to de-icing and anti-icing ability, they also suffer from several significant disadvantages. Any de/anti-icer composition applied to a traveled surface is likely to be washed off the surface by water from melting snow and ice and/or by rainwater. The de/anti-icer composition is thus brought into contact with the wider environment. Ethylene glycol is toxic to humans and numerous cases of poisoning have been reported in the UK and worldwide. Furthermore, ethylene glycol-based de/anti-icers have a high Chemical Oxygen Demand (COD) and thus exhibit deleterious effects when exposed to the wider environment following their application. As a result, the use of ethylene glycol has been prohibited in aircraft de-icing fluids in Europe and at some airports in North America.
Alternative de-icer compositions include those with urea as the active ingredient. However, urea-based de-icer compositions have a highly adverse environmental impact due to their very high COD and by acting as a rich source of nitrogen. Urea-based de-icer compositions are therefore highly damaging to any watercourses which receive run-off from the surface to which the de-icer is applied. In addition, the suitability of urea-based compositions as effective de-icers is compromised by a comparatively high minimum effective temperature of −12° C. (10° F.) which is insufficiently low in colder climates where ground temperatures lower than this minimum effective temperature are often encountered.
In an effort to overcome the disadvantages of ethylene glycol-containing and urea-containing products, de/anti-icing compositions based on 50% w/w aqueous solution of potassium acetate are now used at airports in cold winter climates around the world. Potassium acetate solution can be combined with suitable corrosion inhibitors and meets the high standards of non-corrosiveness to aircraft materials required for airside use, and the COD and Biological Oxygen Demand (BOD) load in water run-off generated by potassium acetate based products is much lower than ethylene glycol or urea-based compositions.
De-icing or anti-icing compositions based on 50% w/w aqueous solution of potassium formate are also used at the airside parts of airports and function in the same way as 50% w/w potassium acetate based fluids but have even lower COD and BOD values.
Embodiments of the present invention can be used in conjunction with such known de-icer or anti-icer compositions (but not exclusively in conjunction with such known compositions) to ensure that only the minimum necessary amount (to achieve the required de-icing or anti-icing effect) of the composition is applied to the traveled surface, thereby to reduce wastage and to avoid or limit possible environmental damage.
A particular problem which arises in relation to the application of de/anti-icer compositions to traveled surfaces is in determining whether an application of the de/anti-icer composition to the traveled surface is, or continues to be, effective. For example, it may be that the de/anti-icer composition is applied to the traveled surface at a given rate appropriate to weather conditions prevailing at the time application, following which the weather conditions become colder, to the extent that the amount of the applied de/anti-icer composition is (at least potentially) insufficient to prevent freezing of water on the traveled surface. Again, it may be that the de/anti-icer composition is applied to the traveled surface at a given rate initially appropriate to prevailing weather conditions, following which there is snowfall and the amount of the applied de/anti-icer composition is (at least potentially) insufficient to melt the snow and prevent its accumulation on the traveled surface. The de/anti-icer composition may be displaced from the traveled surface by the passage of vehicles. Moreover, the de/anti-icer composition applied to the traveled surface may become diluted over time either because of rainfall or by virtue of the melting of the frozen water (ice, snow etc) on the traveled surface by the de/anti-icer composition. Dilution of the de/anti-icer composition reduces the freezing point depressing effect. Also, on dilution, since the de/anti-icer composition becomes dissolved in water on the traveled surface it tends to be carried away from the surface as water run-off. The concentration (amount) of de/anti-icer composition available on the traveled surface for melting (further) ice or snow is thus reduced and the de/anti icing effect correspondingly reduces, or may indeed be eliminated.
As a result, it is important to understand and/or to be aware when the freezing point of liquid on a traveled surface is approaching ambient temperature so that action can be taken to prevent liquid on the traveled surface from freezing. Said freezing point may approach the ambient temperature because of a lessening freezing point depression on dilution of the de/anti-icer moiety and/or because ambient temperatures become colder.
For the above reasons it is important to be able to determine the amount of de/anti-icer composition remaining on a traveled surface at a given time, to be sure that the remaining amount of de/anti-icer composition is sufficient to effect the required degree of de/anti-icing of the traveled surface, taking into account, for example, the likely usage of the traveled surface and the prevailing or expected weather conditions.
However, determining the remaining amount of de/anti-icer composition on the traveled surface is not easy and more especially is not easily achieved in a way which is simple to carry out and which provides reliable results in a short timescale. For example, simple visual inspection of the surface is usually not adequate or reliable as a means of determining whether an appropriate amount of de/anti-icer composition remains on the traveled surface. This can be due to prevailing weather, hours of darkness, or the simple fact that particular de/anti icer material being used is not discernible to the naked eye.
Furthermore, de/anti-icer compositions based on potassium acetate and/or potassium formate are virtually indistinguishable (on visual inspection) from water when on a traveled surface.
Available laboratory methods for analysing freezing point of, for example, potassium acetate or formate concentration of a solution (from which freezing point can be calculated) are not suitable for adaptation to the field environment (i.e. to a traveled surface such as an airport runway), for reasons such as the practical impossibility of collecting suitable samples from the traveled surface, the cost and non-availability of analytical equipment and the non-availability of suitably trained staff. Real-time systems for measuring the potassium acetate or formate concentration in material on the runway surface, based on conductivity probes embedded in the runway surface, have been installed at some airports. The performance and utility of these systems is generally excellent, however such systems are prohibitively expensive for most airports, especially for airports located in areas, such as the U.K, where very cold winters are not an annual occurrence.
Many locations, and most notably airports, therefore, have no sure way of knowing when re-application of a de/anti-icing composition is actually required in winter conditions, and must instead rely mainly or wholly on experience and ‘educated guesses’. This approach is not satisfactory. This approach leaves the airport or other body responsible for the safe operation of a traveled surface at high risk of the traveled surfaces (runways and taxiways) freezing over suddenly. This can lead to accidents such as aircraft overruns or to temporary airport closure. Conversely de/anti-icing compositions will inevitably be applied in circumstances where the application was in fact unnecessary, resulting significant unnecessary expenditure per application, as well as an unnecessary environmental impact even when the de/anti-icer composition is based on materials having a relatively low environmental impact such as acetate or formate.
Embodiments of the present invention, therefore, seek to resolve, or at least mitigate or moderate, the above problems in determining whether, when and/or how much de/anti icer product should be applied or re-applied.